The production of semiconductor wafers, substrates and photomask plates used in the production of semiconductor wafers, has typically utilized processing equipment in which various types of processing fluids are used to treat the wafers. One example of a semiconductor processor is a centrifugal rinser-drier used to rinse acids, caustics, etchants and other processing fluids from wafers, photomask plates, and similar units. The rinser-driers are also used to dry the rinsed units using a flow of heated gas, such as nitrogen, which is passed through the processing chamber after rinsing with the desired fluid. The wafers are spun during processing to provide more even distribution of the processing fluids across the wafer surfaces, and to assist in removal of rinsing liquids in preparation for drying.
Other types of semiconductor processors include acid and caustic treatment tools which spray or otherwise apply acids and caustics to the wafers or other semiconductor-related units. Stripping processors are used to remove photoresist from the wafers. Other specific processing of semiconductors may require other types of chemicals. Many of these processes are appropriately performed in centrifugal processing machines also to provide for even distribution of fluids over the wafer and to aid in removal of liquids.
A primary problem in the production of semiconductors is particle contamination. Contaminant particles can affect the photographic processes used to transfer the chip layouts onto the wafers being processed into chips. Contaminants on the photomasks can cause deterioration of the image being transferred onto the wafer. The direct processing of the wafers themselves is even more susceptible to contamination because of the numerous processing steps which typically occur and the risk at each stage that contaminating particles can become adhered to the surface of the wafer. If the contaminants are present on the surface of the wafer when it is processed in a diffusion furnace, then the contaminants are transferred into the surface of the wafer and cannot in general be removed by subsequent processing. Particle contamination typically causes approximately 50-60% of the chips in a wafer to be defective. Thus it is very important to reduce contamination to increase yields.
Because of the high resolution which has been made possible through newer semiconductor processing techniques, the effects of contaminants has become even more significant and problematic than in the past. Approximately ten years ago contaminant particles smaller than 1 micron were not a problem due to minimum feature sizes of 2 microns or larger. However, now the feature size used in high density chip designs is consistently 0.5 micron. Planning is already progressing for even higher density chips which require feature sizes of approximately 0.3 micron, with even smaller feature sizes expected in the future. The move toward smaller feature size is compounding the contamination problem because of the greater difficulty in controlling smaller particles and the greater numbers of smaller particles. It has been found that the numbers of particles within a given size range is highly non-linear and is believed to approach a geometric relationship. Thus with decreasing feature size the number of contaminating particles which must be controlled or eliminated increases geometrically. If contaminants are present then substantial numbers of the resulting chips can be rendered defective and unusable, at substantial costs to the manufacturer.
The causes of contaminating particles on wafer surfaces occurs from numerous sources. Each of the processing chemicals used is necessarily impure to some small degree. The water used in processing is deionized to remove metallic ions and other impurities, but such supplies also contain some impurities. Also of equal or greater importance is the presence of environmental dust carried in the air in which the wafer is moved between the various processing machines. To reduce this environmental contamination the manufacturers of semiconductors have built production areas which have relatively low amounts of environmental dust. These so-called "clean rooms" are extremely expensive to build and expensive to operate in a manner which maintains contaminant particle levels at acceptably low levels. With the decrease in feature size to provide more dense chips, the difficulties in providing sufficiently low environmental dust levels have increased.
A significant problem in prior art centrifugal processing machines was the need for manual loading and unloading of wafers into these machines. Manual loading was necessary because of the difficulty in accurately placing a wafer carrier containing 20-25 wafers into and out of an enclosed processing chamber of a centrifugal machine which has rotor parts which must accurately position and appropriately maintain the wafers at a desired location for high speed rotation. Manual loading and unloading can significantly slow processing since transfer to the following processing step does not occur when the human operator is occupied with other tasks, such as unexpected problems or other processing equipment. Decreased processing times at each station or machine due to continuing processing improvements further complicates the operator's work and increases the risk that processing rates are limited by manual handling of wafers.
The manual handling of wafers also adversely affects the need for great cleanliness in the processing of such wafers. Properly functioning automated equipment reduces the risks of particle contamination from humans and speeds handling of wafers from one process to the next. It also reduces foot traffic into and around clean rooms which is a significant factor in total processing area contaminant counts.
It has been found desirable to process wafers without handling them in a wafer carrier, as is done in the industry at this time. Wafer carriers are sources of particle contamination. They also present obstructions to rinsing or processing fluid sprays and therefore cause decreased uniformity in the processing of the wafers across the wafer surfaces and from wafer to wafer. Accordingly, the current invention seeks to provide improved processing without utilization of wafer carriers.
Accordingly, there is a substantial need for improved centrifugal semiconductor processing equipment and processing methodologies which can allow efficient automated handling without wafer carriers while maintaining low contamination of the wafers, photomasks or other units being processed.